Photoflash devices of the variety mentioned above typically include a circuit board having an insulative substrate with preestablished circuit patterns or "runs" thereon. Electrically connected at designated locations to this circuitry are a plurality (e.g., eight or ten) of high voltage flashlamps. The circuit board, with flashlamps secured thereto, is located within a suitable, insulative housing having a light-transmitting cover (to permit the high intensity output from each flashlamp to pass therethrough) and at least one connector tab for attaching the device to a respective camera and electrically connecting the circuit board's circuitry to the power source (e.g., piezoelectric element) typically located therein. Activation of the power source by the camera's user, such as by depressing the shutter release button, results in a firing pulse being provided the circuitry and ignition of one of the device's flashlamps. One type of device containing a pair of opposing linear arrays of flashlamps and a singular, common connector tab is referred to in the art as a "flash bar", while another type, which is capable of being inverted and thus possessing two opposing connector tabs, is referred to as a "flip-flash". The " flip-flash" devices were designed primarily to substantially eliminate the photographic phenomenon known as "red-eye", which occurs when light is reflected by the retinae of subjects' eyes onto the photographic film to indicate the eyes' pupils as being red. These latter devices substantially eliminate this possibility by spacing the illuminating flashlamp a specified distance from the camera's lens.
One example of the aforementioned "flash bar" photoflash device is described in U.S. Pat. No. 3,857,667 (J. J. Vetere et al.). An example of an eight flashlamp arrayed "flip flash" is described in U.S. Pat. No. 4,113,424 (D. E. Armstrong et al.), while examples of ten lamp versions of this product are described in U.S. Pat. Nos. 4,152,751 (R. E. Sindlinger et al.) and 4,164,007 (E. G. Audesse et al.). All of the above patents are assigned to the assignee of the instant invention.
As stated, the present invention is concerned with a circuit board assembly which eventually forms an integral part of the final photoflash product. One example of a known technique for making such components (e.g., those used in the aforedescribed "flash bar" device) has been to silk-screen a silver-containing material over a ceramic-coated steel board and thereafter oven-fire the assembly to fuse the silver particles to a continuous conductor. The steel board was originally blanked from a strip of said material, sprayed or dipped with the ceramic, and fired to produce a hardened coating thereon. Silk-screening and oven-firing followed. Another type of technique (e.g., for those components used in many "flip-flash" devices) also involved silk-screening of silver-containing material but instead on a styrene copolymer, thermoplastic substrate (or board). The silver-containing material, applied in paste form, was then subjected to either a radiation curing or hot air drying step. In both of the above examples, the cured silver-containing material served as the conductive circuit in the finished device. Yet another technique (as used in at least one embodiment of a "flip-flash" device) involved approximately the same procedures as used to manufacture circuit board assemblies in such products as television sets. This process required several steps, including photo-resist coating a copper-clad sheet of phenolic or other suitable base material and thereafter chemically removing (e.g., etching) the undesired copper. This component was then thoroughly cleaned and coated with a protective film.
The aforementioned techniques and resulting products contain several disadvantages. Silk-screening, for example, requires utilization of pastes which in turn are comprised of discrete silver particles located therein and separated by a binder. Although these pastes are eventually subject to some form of heat treatment to hopefully fuse said particles, the finished circuitry understandably is limited in its conductivity (and thus possesses an inherently higher resistance) in comparison to conductors presented in another state. Silk-screened circuitry is also susceptible to containment of discontinuities as might result from dust or lint interference during the screening operation. The presence of a screened silver layer also poses a problem when the chosen method for securing the device's flashlamps to the circuitry is soldering. Occasionally, the silver layer has prevented proper wetting during this process. Still another inherent problem with silk-screening conductive circuitry is the ready opportunity for dimensional impreciseness due to the horizontal flow (beneath the screen) as the paste is forced through the screen's pattern. In addition, occasional smearing of the circuit run is practically unavoidable. The latter problems are particularly troublesome to devices employing high voltage flashlamps in that sparkover can then occur between the circuit's elements, resulting in either product failure or simultaneous flashing of two or more lamps. A final disadvantage of the above processes is the relatively high costs associated therewith. Techniques using photo-resist coating, development, and subsequent chemical removal are understandably costly in terms of both time and material. Silk-screening is also understandably costly, particularly as a result of using the precious metal silver and the relatively rapid wear of the screen materials typically used in this process.
The present invention overcomes the several, aforementioned disadvantages by providing a circuit board assembly wherein the technique of die-stamping is utilized to accurately define and position a conductive circuit on an insulative substrate without the need for photo-resists, chemical echtants, precious metals, etc. In addition to this, and of equal or greater significance, this technique as utilized in the present invention defines a procedure whereby the device's circuit runs (or paths) can be satisfactorily positioned and electrically connected to other elements which also constitute part of the device's circuitry without causing damage thereto. One primary example of such an element as utilized in today's more recent products is a radiation sensitive switch which is usually electrically connected in series with a respective flashlamp and adapted for receiving the radiant energy from the lamp upon ignition thereof. The switch will thus melt or shrink to define an open circuit almost instantaneously after flashlamp ignition and thereby permit reliable flashing of the subsequent lamps in the device's array in rapid succession An example of a radiation sensitive switch is described in U.S. Pat. No. 4,017,728 (E. G. Audesse et al.), which is also assigned to the assignee of the present invention. As described therein, these switches each are typically comprised of a thin strip of polymeric material attached to the circuit board across a respective aperture provided therein. A typical ten-lamp array will include eight switches of this variety in view of the obvious understanding that the last fired lamp on each end of the array has no need for such an element. It is understood that the relatively delicate nature of such elements as radiation sensitive switches does not readily permit electrical connection thereto by a technique as relatively severe and demanding as die-stamping. Die-stamping has been utilized in the production of printed circuit components for use in other types of products than those described above but only because such components (and therefore products) did not require elements such as radiation sensitive switches therein. Typically, these products consisted of only a base or substrate, a solid metal conductor (e.g., copper foil), and a bonding adhesive. See, e.g., U.S. Pat. Nos. 3,911,716 (W. Weglin) and 3,990,142 (W. Weglin). The invention as will be described is thus deemed all the more unique and significant in that it not only assures positive electrical connection between the component's circuit runs and delicate switch elements but also provides for definition and securement of the circuit runs to the insulative substrate which forms an integral part of the final product.
It is believed therefore that circuit board assemblies produced in accordance with the techniques defined herein will constitute significant advancements in the art.